Slippage recorder



July 21, 1942.

G.' P. BosoMwoRTH SLIPPAGE RECORDER Filed 001'.. 4, 1959 7 sheets-sheet.1

INVENTOR ji BY w ig/a ATTORN EYS July 21,1942- G. P. BOsoMwoRTH2,290,618

SLIPPAGE RECORDER Filed oct. 4, 1959 7 sheets-sheet 2 INVENTOR ATTORNEYSJuly 21, 1942. Q p, BQSQMWQRTH v 2,290,618

SLIPPAGE RECORDE R Filed oct. 4, 1939 '7 sheets-sheet 3 (@IIIIQ) vINVENTOR je 1p, a/a/m//az/ ATTORNEYS G. P. BosoMwoRTH SLIPPAGE RECORDERFiled OCT.. 4, 1939 @M 7 Sheets-Sheet 4 ATTORNEYS Juli 21,1942 G. P.BosoMwoR'rH 2,290,518

SLIPPAGE RECORDER l Filed Oct. 4, 1939 7 Sheets-Sheet 5 INVENTOR `EN l.

July 21, 1942.

G. P. BosMwoRTl-l 2,290,618

'sm-PAGE RECORDER Filed oct. 4, 19:59 l

A'7 Sheets-Sheet -6 R o T N E V m lli fear @p/awww@ ATTORNEYS July 211942 G. P. BosoMwoRTl-l 2,290,618`

I SLIPPGE RECORDER Filed 0G12. 4, 1959 7 ShetS-Sh6et 7 INVENTORATTORNEYS Patented July 2l, 1942 SLIPPAGE RECORDER George P. Bosomworth,Akron, Ohio, assignor to The Firestone Tire & Rubber Company, AkronOhio, a, corporation of Ohio Application October 4, 1939, Serial No.297,914

(Gl. Z3-5l) 11 Claims.

This invention relates to slippage recorders, and more especially itrelates to instruments for graphically recording the slippage orrelative movement between two frictionally engaged surfaces. Theinvention is of utility in a number of situations, as for example, forrecording the relative movement between a conveyor belt and a continuouslength of material being fed onto one end thereof, or for recording theslippage between a driven vehicle wheel and the surface over which it isbeing driven.

Solely for illustrative purposes, the invention is shown in theaccompanying drawings in its adaptation to the recording of slippagebetween a tractor tire and the roadway or ground over which the tractoris being driven. Such slippage represents a loss of traction and, in thelast analysis, an economic waste. It is common practice to endeavor toreduce slippage loss by the provision of improved traction elements onthe tires with which a tractor is equipped, so that by the use of theinvention it is possible to obtain comparative data on the tractivequalities of various tire designs.

The chief objects of the invention are to provide a slippage recorder ofthe character mentioned that will be relatively simple in itsconstruction and operation; that will provide a graphic record ofresults obtained; and that operates from the wheel rather than from thetire being tested. Other objects will be manifest as the specificationproceeds.

Of the accompanying drawings:

Figure 1 is a perspective view of a tractor and a trailer attachedthereto, and the improved slippage recorder operatively associatedtherewith to record the slippage of one of the tractor tires;

Figure 2 is a plan view of a iifth wheel attached to the rear end of thetrailer;

Figure 3 is a side elevation of the structure shown in Figure 2;

Figure 4 is a plan view of a housing carried bv the framework of thefifth wheel structure, the cover f said housing being removed to showtherein one unit of a pair of self-synchronizing motors;

Figure 5 is a section on the line 5-5 of Figure 4;

Figure 6 is a front elevation of the recording instrument of theapparatus; v

Figure 6A is an isolated elevational detail, on a smaller scale, of themechanism immediately connected to the recording finger of the devicefor operating the same.

Figure 7 is a side elevation thereof as viewed from the right of Figure6;

Figure 8 is a section on the line 8-8 0f Figure '7;

Figure 9 is a side elevation of the recording the Shaft 32 is providedinstrument as viewed from the left of Figure 6, parts being broken awayand in section;

Figure 10 is a section on the line l El-l of Figure 11 showing a switchmechanism;

Figure 11 is a section thereof on the line M l of Figure 10;

Figure 12 is a section on the line lE-l of Figure 11; and

Figure 13 is a wiring diagram of the slippage recording apparatus.

Referring first to Figure 1 of the drawings, there is shown a motorpropelled tractor I5 that is drawing a wheeled trailer l hitched to therear thereof. The tractor is of the type that has four wheels whereofthe two rear wheels are power-driven, said wheels being provided withrespective pneumatic tires Il. It is the function of the apparatusconstituting the subject matter of this invention to measure theslippage between the tires Il and the ground over which they travel tothe end that the tractive value of the lugs or characters on the treadof the tires may be determined. v

Swiveled to the rear end of the trailer It is a frame 2li that iscapable of oscillating movement in a vertical plane, and journaled insaid frame is a wheel 2| equipped with a pneumatic tire 22, Theoscillating feature of the frame 2i! enables the tire 22 to maintaincontact with the ground or roadway at all times, and since no drivingtorque is applied to the wheel 2l, there will be no slippage of the tire22 upon the ground or roadway. Preferably the frame 2t is so constructedthat the tire 22 is laterally offset with relation to the centerline ofthe tractor and trailer and travels in the track of one of the tires Il,being thus subject to the same irregularities of the roadway as thelatter;

The hub of the Wheel 2| is provided with a bevel gear 24, Figures 2 and3, and meshed with said gear is a bevel pinion 25 carried upon one endof a shaft 26, the latter being journaled in a pair of bearing brackets21, 21 carried by the frame The other end of shaft 2B extends into a boxor housing 28 that is supported upon framework 2li, forwardly of thewheel 2l, said shaft being supported by a journal bearing 29 therein andhaving its end portion connected to one element Si! of a free-wheelingclutch of the usual or preferred type. The other element 3l of saidclutch is mounted upon the adjacent end of a short shaft 32 that is inaxial alignment with shaft Zi, and is journaled in a suitable bearing33. At its end remote from clutch element 3| with a gear 3d that ismeshed with a pinion 35 mounted upon the rotor shaft 38 of a motor 37.The latter is one of a pair of self-synchronizing motors of the typemarketed under the trade name of Autosyn, and are provided for thepurpose of remote control. They operate on the principle of electricalbalance, which causes the synchronous motors, whose fields are excitedfrom the same A. C. source of power, to assume the same geometricalposition. The location and function of the second synchronous motorpresently will be described. The arrangement is such that the rotatingwheel 2| drives the motor 31 through the agency of shaft 25, clutch 3i),3|, gear 34, and pinion when the tractor i5 and trailer i6 are movingforwardly, the clutch preventing the driving of the motor when the truckand trailer are moving rearwardly. From the foregoing it will beapparent that the rotary speed of the motor 31 is in direct ratio to thespeed of rotation of the wheel 2| at all times and at all speeds of thevtrailer and tractor.

The recording instrument of the apparatus for convenience may be mountedupon the trailer i6, as shown in Figure l. Said instrument is designatedas a whole by the character R, and is shown in detail in Figures 6 to` 9inclusive. The recording instrument comprises a suitable base plate uponwhich is carried the framework 4| of the instrument. Mounted at the topof said framework is an electric motor 42 that is arranged on a verticalaxis, and which drives a reduction gear device (not shown) mounted in acasing 43 below said motor. Said reduction gear device drives twovertical shafts 44, 45, Figure 6, that are driven in opposite directionsand which project below the casing 43, said shaftsV being provided withrespective gears 45, 41 that are positioned in different horizontalplanes, which planes arespa-ced apart from each other. The

motor 42 is driven by means of a standard 6 volt storage battery 48,Figure 13, which battery may be carried at any convenient place in thetrailer IG. rhere is a control switch 49 in the circuit of the motor 42and battery 48, and speed of the motor is controlled by a rheostat 55,the latter being enclosed in a casing 5| on the framework 4| andprovided with an adjusting knob 52 on the exterior of its casing.

The function of the motor 42 is to drive a pair of spools 54, 54 aboutwhich a recording chart 55 passes, the rotation of said spools movingsaid chart longitudinally in a manner subsequently to be explained. Thespools 54 are parallel and are positioned below the motor and thereduction gear device. They are mounted upon respective vertical shafts5t that are journaled at their opposite ends in suitable bearings, suchas the bearing 51,. Figure 9, said bearings being supported in theframework 4 I.. ings, above the spools 54, each shaft 56 is providedwith a gear 51, which gears are in mesh with an intermediatelypositioned gear 58. As is best shown in Figure 9, the gear 58 is mountedupon the lower end of a short vertical shaft 59 that is journaledintermediate its ends in bearings Sil that are mounted in framework 4|,the upper end portion of the shaft being provided with a gear E i.

Also pivotally mounted upon the upper end portion of shaft 55, forangular movement in a horizontal plane, is a lever` 54, which lever isdisposed above the gear 5i. Botatably mounted upon the under side oflever 64 is a pinion B5, Figure 8, that is meshed with gear 6|. Alsomounted upon the under side of lever 54, remote from pinion S5, is asecond pinion 65, the latter being meshed with gear 6|, and also meshedwith a gear 61. The gear 51 is carried upon the lower end of a shortvertical shaft S8 that is jour- Adjacent their upper bearnaled in lever64, said shaft extending through said lever and being provided with arelatively small pinion 69 on its upper end. The lever 64 is movableangularly about the shaft 59, and has two alternative positions, in oneof Which positions it is shown in Figure 8. The said lever carries aspring pressed bolt that is operated by the knob 'i0 on the free end ofthe lever, said bolt being insertable in apertures, such as the aperture1|, Figure 8, for retaining the lever` in its alternative positions.When the lever is in the position shown in Figure 8, the pinion 65 is inmesh with the driving gear 46, and the spools '54 are driven thereby.When the lever is in its alternative position, the pinion 69 is in meshwith driving gear 41 with the result that the spools 54 are driven inthesame direction as previously, but at determinately slower speed. Thearrangement is such that the feed of the chart 55 may be correlated withthe speed of the tractor I5. A backing plate 12 is mounted in front of-the crevice between the spools 54, being secured at top and bottom tothe framework 4|. The chart 55 passes over said backing plate 12 inmoving from one spool 54 to the other, and thereby is given lateralsupport to facilitate the scribing of a line record on the chart.

The spools 54 serve only to drive and guide they chart 55, the latterbeing initially in a roll 14 that is mounted upon a supply-spool 15, andbeing Withdrawn lfrom the latter and rewound upon a re-wind spool 16,after passing across the backing plate 12. The spools 15, 16 aredis-posed rearwardly of the spools 54, and are carried by respectiveC-shaped brackets 11, 11, that are of identical construction. Each ofthe brackets 11 is positioned between `parallel plates or shelvesconstituting a .part of the framework 4|, and is slidably mounted so asto enable it to be urged in the direction of a spool 54 for a purposepresently to be explained. For guiding the brackets 11Y during suchsliding movement, each is provided at its top with an upwardlyprojecting pin 18, Figure 8, that is engaged in a slot 15 in the upperparallel plate aforementioned. In like manner the bottorn of eachbracket is provided with a down wardly projecting pin Sil, Figure 9,engaged in a slot 8|' in the lower parallel plate.

The spools 15, 16 are removably mounted in the brackets 11 so as to bereplaceable with fresh supply and rewind spools whenever the chart 55 iscompletely wound upon the latter. To this end both laterally extendingarms of each of said brackets has a sleeve 84 fixedly mounted therein,the sleeves of each bracket being axially aligned. As shown in Figure 9,each sleeve has an axially movable spindle 85 mounted therein, whichspinle is circumferentially grooved at axially spaced apart points toreceive a spring-backed detent 85 that serves to hold the spindle in oneof two alternative positions. The outer end portion of each sleeve 84projects beyond the bracket and extends through a slot 81 in theframework plate, said slot being parallel to and in alignment with aslot 19 or 82|. The inner end of each spindle 85 is of reduced size, asshown at 88, and is inserta-ble into an axial bearing 89 carried at oneend of the spool 15 or 15. The outer end of each spindle 35 is providedwith a knob 90 that may be grasped to pull the spindle axially, wherebyits reduced inner end portion may be withdrawn from the bearing 89 ofthe spool, thus enabling the spool to be removed for the purposepreviously set forth. Fixedly mounted upon each sleeve 84, above andbelow the spools 15, 16, are

grooved sheaves 93, 93, about which are trained respective endless belts94 consisting of helically coiled spring wire, said belts also beingtrained about respective sheaves 95 carried by the adjacent shafts 56,above and below the spools y54. The s-pring belts 94 serve to urge thespools 15, 16 against the driven spools 54, so that rotation of thelatter Will drive said spools 15, 16. A friction brake 15a, Figure 7,engages the lower end of the spool 15 to retard rotation of the same andthus to assure that the chart 55 will be withdrawn from the supply roll14 thereon under sufficient tension to cause it to lie fiat against thebacking plate 12. The slots 81 are formed at their ends remote from thespools 54 with respective laterally offset portions 81a, Figure 8, intowhich the sleeves 84 may be moved while the spools 15, 16 are beingremoved from the device, upon oc-casion, as when a completed chart isIbeing removed and a new supply roll 14 of chart material is beingplaced in the device.

Mounted upon the base plate 40 is a self-synchronizing moto-r 96, whichis the receiving motor of the self-synchronizing motor 31 hereinbeforedescribed. The motors 31, 96 are electrically connected to each other inthe usual manner, as shown in Figure 13, and are excited by the same A.C. source of power, namely, a rotary converter 91, the latter beingdriven by a heavy duty storage battery 98, Figure 13. The rotaryconverter 91 and storage battery 98 are of standard construction andneed no further illustration or description. They may be installed atany convenient place in the trailer I6. The arrangement is such that therotors of the synchronous motors assume the same geometric positions 'atall times.

The shaft of the motor 96 is provided with a gear that is meshed with anidler pinion |0| that is suitably journaled in a bearing bracket |02carried by the framework 4|. Also journaled in said bearing bracket |02is a short shaft |03, one end of which carries a gear |04 that is meshedwith pinion |0|, the gear |04 being considerably larger than gear |00 toprovide substantial speed reduction between the motor 96 and shaft |03.The other end of shaft |03 is connected to one element of a magneticclutch |05, the other element of which is carried by a shaft |06 that isaxially aligned with shaft |03 and also carried in the bearing bracket|02. The shaft |06 carries a grooved pulley |01 about which is trained anarrow belt |08 of wire or strong cord, said belt also passing overanother pulley |09 that is mounted at an elevated position beside thegear casing 43, said pulley |09 being journaled upon an upright bracketH0, Figure 6, carried by the framework 4|. The belt |08 is xedly securedto the pulley |01 by means of a set screw lll, thereby obviating anypossibility of slippage therebetween. One reach of the belt |08, (thefar reach as viewed in Figure 6) has a metal rod l |'2 interposedtherein, and xedly secured to said rod is a laterally projectingrecording finger ||3 that extends in front of the chart 55, the free endof said finger overlying the backing plate 12 and being provided withany suitable scribing device, such as a pen indicated at I4, Figure 6.For holding the pen firmly against the chart, the finger 3 is formedintegrally with an extension ||3a that extends in the opposite directionfrom the rod ||2 and slidingly bears against a plane vertical guide barthat is carried by the bracket H0, said guide bar having lateralprojections IIS, ||`1 at top and bottom thereof that are engageable bythe finger-extension I |3a, and which constitute stops to limit theupward and downward movement of the nger. The near reach of the belt |08extends through an aperture H9, Figure 6A, in the framework 4|, and isconnected to the upper end of a tension spring |20, the lower end of thelatter `being connected to a fixed point |2| on said framework.

The arrangement is such that the constantly driven motor 96 drives thegear |04 and shaft |03 in the direction indicated by the arrow in Figure7, thereby driving the shaft I 06 and pulley |01 through the agency ofthe normally closed magnetic clutch |05, with the result that the rod||2 and recording finger I3 are moved downwardly against the tension ofthe spring 20, and the pen on said finger scribes a substantiallyvertical line on the slowly moving chart 55. Opening of the magneticclutch |05 disengages driven shaft |06 from the driving shaft |03,thereby enabling spring |20 to reverse the movement of the belt |08 andpulley |01, and to restore the finger ||3 the top of chart 55. Openingof the magnetic clutch |05 is effected periodically and automaticallythrough the agency of a normally closed timer switch in the electricalcircuit of the said clutch, said switch being operated by the drive ofthe tractor l5.

Although the timer switch may be mounted at any convenient place on thetractor, satisfactory results have been obtained when it has beenmounted upon the propeller shaft housing, in engagement with the end ofthe propeller shaft and it is so illustrated in Figures 10 to 12 of thedrawings to which attention now is directed. As shown in Figure 11, |24is the rear end of the propeller shaft of the tractor, and |25 is aportion of the housing enclosing the same. Mounted upon the exterior ofthe housing |25, in axial alignment with the shaft |24, is a timercasing comprising a base casting |26 that is secured to the housing |25by bolts |21, |21, and a removable sheet metal cover |28 of circularshape that is secured to base |28 by set screws |29, |29. Diametricallyspanning the base casting |26 is a bridge-like bearing structure |30that constitutes an end bearing for the outer end of an axial shaft |3|,the inner end portion thereof extending through a stuiiing box,designated as a whole by the numeral |32, which stuing box is carried bythe housing 25. The inner end portion of shaft |3| is disposed withinthe housing |25 and is provided with a short crank |33 that is radiallyslotted at |34 to receive a crank pin |35 that is mounted in the end ofthe propeller shaft |24, eccentrically of the axis thereof. Thearrangement is such thatrotation of propeller shaft |24 drives the shaft|3|, in counterclockwise direction as viewed in Figure l0.

Mounted upon shaft |3|, below bearing structure |30, is a gear |38 thatis meshed with an idler pinion |39, the latter being meshed with a gear|40 that is journaled upon a stub shaft 4| that projects from the basecasting |26 in which it is secured. The idler pinion |39 is journaled atthe free end of a supporting arm |42 that is bolted to the base casting|26, said bolts extending through respective longitudinally disposedslots |43 in the arm to enable adjustment thereof. The arrangementenables the changing of gears |38, |40 to obtain the desired speedreduction therebetween. Also journaled upon the stub shaft |4|, behindgear |40, is a to elevated position at cam hub |44 that has drivingconnection with said gear through the agency of a pin |45. The cam hub|44 is formed with a circumferential radial fiange |45 to which issecured by means of set screws |41, liti, a fixed disc cam |48 and anadjustable disc cam |49, the latter being formed, with arcuate slots|59, |59 through which the screws |41 extend, thereby enabling cam |49to be adjusted angularly relatively of cam |43. The peripheral camsurfaces of the cams |48, |49 are identical, each comprising an elevatedregion of 390 extent and a lower or depressed region of 60 extent. Byadjusting cam |49 angularly relatively of cam |48 the linear extent ofsaid depressed region may be reduced, as is clearly shown in Figure 10.

Engaging the perimeter of the cams |49, |49 is a cam roller |52 that isjournaled in one end of a cam lever |59 that is journaled at anintermediate point |54 upon the base casting |25. A tension spring |55connected to the cam lever and to a fixed point |55 on the base castingnormally yieldingly urges the cam lever in the direction that holds thecam roller |52 against the cams. The other end of the cam lever isprovided with an adjustable screw |51 that is engageable with the pushbutton |58 of an electrical switch |59, Figure 13, that is in theelectrical circuit of the magnetic clutch |05, the battery 93 also beingin said circuit. The switch |59 is enclosed in a suitable, switch-box|60 mounted upon the base casting |26 of the timer device. Said switchis so constructed that it closes the electrical circuit to the clutch|95, thus actuating or engaging the elements of the latter, when the camroller |52 is on the elevated region of the cams |48, |49 as shown inFigure l0, and opening to effect the disengaging of the elements of saidclutch when the cam roller is on the depressed region of the cam, asshown in Figure 1'3.

In the operation of the embodiment of the device illustrated, tires |71to be tested for slippage are mounted upon the tractor I5, and a controltire, preferably of the same diameter, is mounted in the trailing frame29. The switch 49 is closed to set the chart motor 42 in motion, toeffect longitudinal movement of the chart 55. Switch |59 is normallyclosed, thus closing the magnetic clutch |95 and causing indicatorfinger ||3 to move downwardly whenever the synchronous motor 99 is inmotion. When making a test, the tractor I is driven forwardly, thusdrawing the trailer affter it and thus causing rotation of trailingwheel 2| with tire 22 thereon. As soon as the tractor is in motion, therotary converter 9i is put into operation to effect the driving of thesynchronous motors 31 and 95, the rotors of said motors maintaining thesame geometric -position at all times. For this reason the downwardmovement of the indicator finger always will bear the same determinaterelation to the angular position of the wheel 2| notwithstanding thevariations of speed to which the latter may be subject. The drive of thetractor effects the rotation of the cams |135, |49 and thereby effectsperiodic opening of the switch |59, satisfactory results having beenobtained when the cams are driven at such speed as to make onerevolution every two seconds. Opening of switch |59 de-energizesmagnetic clutch |05 thereby disengaging the shaft |96 from drive shaft|53, thereby enabling spring |29 to return the indicator finger ||3 to adeterminate elevated position. Thus it will be seen that the pen ||i4onthe end of finger |.|3 will scribe a curve on the moving chart 55, andthat the finger will oscillate, that is, move up and down at a frequencythat is in direct ratio to the speed of rotation' of the driven wheel2|. The

, instrument is so regulated that the finger may have maximum amplitudeof movement within the lateral margins of the chart 55. Maximumlamplitude of movement of the ringer ||3 is possible only when there isno slippage -between the tires and the roadway, for such slippageaccelerates the rotation of the cams |48, |49 and thus causes the fingerI3 to rise before reaching the extremity of its downward movement, thecurve scri-bed by the 4pen ||4 being thereby modulated. By comparing theenvelope of the modulated curve with a curve scribed by the indicatorfinger moving at maximum amplitude, the percentage of slippage of thetires 4may be computed.

The slippage data thus obtained, to be acceptable as an accurateindication of the tractive characteristics of tires, must be consideredin connection with other factors that influence slippage. Thus loaddrawn by the tractor must be uniform and constant, and the speed of thetractor also must be considered. Apparatus for maintaining a determinateand constant Ipull on the drawbar of the tractor, and for indicating thespeed thereof are provided, but such apparatus is no part of the presentinvention and needs no further disclosure herein.

The recording instrument shown at |55 of the drawings is operated by theengine of the tractor and forms no part of the present invention.

The invention is automatic in its operation, it providesa graphic recordof the slippage of the tractor wheels, and achieves the other objectsset out in the foregoing statement of objects.

Modification -may be resorted to without departing from the spirit ofthe invention, or the scope thereof as defined by the appended claims.

What is claimed is:

l. In a device for recording slippage between the driving wheels of avehicle and a roadway, the .combination of an indicating mechanismcomprising a continuous, moving recording chart and a recording fingermovable thereover, a driven wheel connected to the vehicle and rotatedby 'being drawn over the roadway, means for moving the recording fingerover the chart in one direction at a speed proportional to the speed ofrotation of said wheel, and means controlled by the rotation of thedriving wheels of the vehicle operating periodically to limit theamplitude of movement of said recording finger and to return the fingerto point of starting.

2. In a device for recording slippage between the driving wheels of avehicle and a roadway, the combination orf an indicating mechanismcomprising a continuous, moving chart and a recording finger movablethereover, a driven wheel connected to the vehicle and rotated by beingdrawn over the roadway, means operatively connecting the driven wheelwith the recording finger for impelling the latter over the ychart inone direction, and means controlled by the rotation of the drivingwheels for periodically disconnecting the indicating finger from saidimpelling means whereby the amplitude of movement of the recordingfinger is proportional to the relative rotation between the driving anddriven wheels.

3'. In a device lfor recording slippage between the driving wheels of avehicle and a roadway,

the combination of an indicating mechanism comprising a continuous,moving chart and a recording finger movable thereover, a driven wheelconnected to the vehicle and rotated by being drawn over the roadway,means operatively connecting the driven wheel with the recording fingerfor impelling the latter over the chart in one direction, yielding meansopposing said movement of the recording finger, and means controlled ,bythe rotation of the driving wheels of the vehicle for periodicallydisengaging the indicating nger from said impelling means to enable theyielding means to return the finger to original position whereby theamplitude of movement of the recording finger is proportional to therelative rotation between the driving and driven wheels.

4. In a device for recording slippage Ibetween the driving wheels of avehicle and a roadway, the combination of an indicating mechanismcomprising a continuous, moving chart and a recording finger movablethereover, a driven wheel connected to the vehicle and rotated byfriction of the roadway, means operatively interposed between the drivenwheel and the recording finger for impelling the latter over the chartin one direction, said means comprising a releasable connection, andmeans controlled by the rotation of the driving wheels of the vehiclefor periodically releasing said connection as a means of modulating theamplitude of movement of said recording finger, the said amplitude ofmovement being proportional to the slippage'between the driving wheelsand the roadway.

5. In a device for recording slippage between the driving wheels of avehicle and a roadway, the combination of an indicating mechanismcomprising a moving chart and a recording finger movable thereover, adriven wheel connected to the vehicle and rotated by friction of theroadway, means operatively interposed between the driven wheel and therecording finger for impelling the latter over the chart in onedirection, said means comprising a normally energized magnetic clutch,and means controlled by the rotation of the driving wheels of thevehicle for periodically de-energizing said clutch to disengage saidfinger from its impelling means, thereby modulating the amplitude ofmovement of said finger under impetus of said impelling means, the saidamplitude of movement being proportional to the slippage between thedriving wheels and the roadway.

6. A combination as defined in claim 5, including spring means opposingthe impelling movement of the recording finger, and returning the latterto point of starting when the clutch is deenergized.

7. In a device for recording slippage between the driving wheels of avehicle and a roadway, the combination of an indicating mechanismcomprising a continuous, moving chart and a recording finger movablethereon, a driven wheel connected to the vehicle and rotated by frictionof the roadway, a pair of self synchronizing electric motors operativelyconnected with said driven wheel and recording nger respectively forimpelling said recording finger in one direction in determinate relationto the rotation of said wheel, and means controlled by the rotation ofthe driving wheels for periodically disengaging said recording nger fromits impelling means whereby the amplitude of movement of the recordingfinger is proportional to the slippage between the driving wheels andthe roadway.

8. In a device for recording slippage between the driving wheels of avehicle and a roadway, the combination of an indicating mechanismcomprising a continuous, moving chart and a recording finger movablethereover, a driven wheel connected to the vehicle and rotated byfriction of the roadway, a pair of self synchronizing electric motorsoperatively connected with said driven wheel and said recording ngerrespectively for impelling said recording finger in one direction indeterminate relation to the rotation of said wheel, yielding meansoperating in opposition to said movement of the recording finger, andmeans controlled by the rotation of the driving wheels for periodicallydisengaging said recording finger from its impelling means, therebyenabling said yielding means to retract said recording finger, wherebythe amplitude of movement of the recording finger is proportional to theslippage between the driving wheels and the roadway.

9. In a device for recording slippage between the driving wheels of avehicle and a roadway, the combination Aof an indicating mechanismcomprising a continuous, moving chart and a recording finger movablethereover, a driven wheel connected to the vehicle and rotated byfriction of the roadway, a pair of self synchronizing electric motorsoperatively connected with said driven wheel and said recording iingerrespectively for impelling said recording finger in one direction indeterminate relation to the rotation of said wheel, a normally energizedmagnetic clutch in the finger-impelling mechanism, a switch controllingthe operation of said magnetic clutch, and means operated by thepropelling mechanism of the vehicle for periodically operating saidswitch, whereby the amplitude of movement of the recording nger isproportional to the relative rotation of the driving and driven wheels.

10. A device for recording relative movement between a movable drivingmember and a movable driven member caused to move due to movement ofsaid driving member, said` device comprising said driven member, achart, a recording finger movable transversely of said chart, meanscontrolled by movement of one of said members for moving the fingeracross the chart in one direction, and means controlled by the othermember for terminating the said movement of the recording finger andreturning it to its point of starting after said one member has moved adeterminate extent whereby variation in the amplitude of movement of therecording finger is proportional to the relative movement of saidmembers.

11. A device for recording relative rotation between a rotatable drivingmember and a rotatable driven member caused to rotate due to rotation ofsaid driving member, said device comprising said driven member, amovable chart, a recording finger movable transversely of said chart,means controlled by the rotation of one of said members for moving thefinger across said chart in one direction and means controlled by theother member for terminating the said movement of the recording fingerand returning it to its point of starting intermittently as said othermember makes a determinate number of revolutions, whereby variation inthe amplitude of movement of the recording finger is proportional to therelative rotation between said members.

GEORGE P. BOSOMWORTH.

